Alkaline earth metal zirconium oxide additive useful for improving ballistic performance of gas generating compositions

ABSTRACT

A gas generant composition for an automotive inflatable restraint system includes one or more: fuels, such as guanidine nitrate; oxidizers, such as basic copper nitrate; and an alkaline earth zirconium oxide. The gas generant composition is substantially free of potassium perchlorate. The alkaline earth zirconium oxide may be barium zirconate (BaZrO 3 ), calcium zirconate (CaZrO 3 ), and/or strontium zirconate (SrZrO 3 ). The alkaline earth zirconium oxide may be present at ≥about 0.1% by mass to ≤about 6% by mass of the gas generant composition. Such gas generants may be cool burning (e.g., a maximum flame temperature at combustion (T c ) of ≤about 1700K (1,427° C.)), have a linear burn rate of ≥about 20 mm per second at a pressure of about 21 MPa and a linear burn rate pressure exponent (n) of ≤about 0.35. Method of making such gas generants are also provided.

FIELD

The present disclosure relates to an additive that is useful for improving ballistic performance of gas generating compositions.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

Passive inflatable restraint systems minimize occupant injuries in vehicles by using a pyrotechnic gas generant to inflate an airbag cushion (e.g., gas initiators and/or inflators) or to actuate a seatbelt tensioner (e.g., micro gas generators), for example. Suitable gas generants provide sufficiently high gas output at a high mass flow rate in a desired time interval to achieve a required work impulse for the inflating device. Certain gas generant pyrotechnic compositions comprise a fuel, such as guanidine nitrate (GuNO₃) and an oxidizer, such as basic copper nitrate (bCN), which provide excellent properties, including good molar gas yield (in term of moles generated per 100 g) and volumetric gas yield (in terms of moles of generated per 100 cc). Moreover, such gas generants comprising guanidine nitrate and basic copper nitrate are considered to be cool burning, for example, having a maximum combustion temperature of less than or equal to about 1700 K (1,427° C.). It is desirable to have such a gas generant formulation combust at sufficiently rapid burn rates with minimal pressure dependence, to allow it to be employed in a variety of practical airbag inflation applications.

In order to achieve high burn rates with minimal pressure dependence, conventional pyrotechnic gas generants comprising guanidine nitrate and basic copper nitrate typically employ a ceramic type additive. Common examples of ceramic type additives include silicon dioxide, aluminum oxide, and various clays or glasses. Such ceramic additives improve burning rate and reduce pressure sensitivity, as well as provide slagging capability by serving as a solid nucleus for condensing and capturing combustion by-products that are liquid (or semi-solid) during the combustion process. The burning rate and pressure exponent of gas generating compositions comprising guanidine nitrate and basic copper nitrate with such ceramic type additives are typically less than 20 mm/s (e.g., typically around 17 to 18 mm/s) at 21 MPa with a pressure exponent of greater than or equal to about 0.4. It would be desirable to develop gas generant compositions that comprise guanidine nitrate and basic copper nitrate, but further have higher burn rates and reduced pressure sensitivity expressed by a lower pressure exponent.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Advantageously, the present disclosure in certain variations provides gas generant compositions for an automotive inflatable restraint system. The gas generant composition may comprise one or more fuels, one or more oxidizers; and an alkaline earth zirconium oxide. Furthermore, the gas generant composition is substantially free of potassium perchlorate.

In one aspect, the alkaline earth zirconium oxide is selected from the group consisting of: barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof.

In one aspect, the alkaline earth zirconium oxide is present at greater than or equal to about 0.1% to less than or equal to about 6% by mass of gas generant composition.

In one aspect, the alkaline earth zirconium oxide is present at greater than or equal to about 0.5% to less than or equal to about 5% by mass of the gas generant composition.

In one aspect, the gas generant composition has a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa).

In one aspect, the gas generant composition has a linear burn rate pressure exponent (n) of less than or equal to about 0.35.

In one aspect, the gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1700K (1,427° C.) and a gas yield of greater than or equal to about 5.7 moles/100 cm³.

In one aspect, the gas generant composition is substantially free of silicon dioxide, aluminum oxide, and combinations thereof.

In one aspect, the one or more fuels are selected from the group consisting of: guanidine nitrate, diammonium 5,5′-bitetrazole (DABT), copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, a melamine oxalate compound, and combinations thereof. The one or more oxidizers are selected from the group consisting of: basic copper nitrate, alkali metal or alkaline earth metal nitrates, alkali metal, ammonium perchlorate, metal oxides, and combinations thereof.

In one aspect, the one or more oxidizers comprises ammonium perchlorate at less than or equal to about 7% by mass of gas generant composition.

In one aspect, the one or more fuels comprise guanidine nitrate present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition. Basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition. The gas generant further comprises one or more gas generant additives present at greater than or equal to 0% to less than or equal to about 8% by mass of the gas generant composition.

Advantageously, the present disclosure in certain other variations provides gas generant compositions for an automotive inflatable restraint system. The gas generant composition may comprise guanidine nitrate, basic copper nitrate, and greater than or equal to about 0.1% to less than or equal to about 6% by mass of barium zirconate (BaZrO₃). The gas generant composition is substantially free of potassium perchlorate.

In one aspect, the barium zirconate (BaZrO₃) is present at greater than or equal to about 0.5% to less than or equal to about 5% by mass of the gas generant composition.

In one aspect, the gas generant composition has a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent (n) of less than or equal to about 0.35.

In one aspect, the barium zirconate (BaZrO₃) is present at greater than or equal to about 4% to less than or equal to about 5% by mass of the gas generant composition. The gas generant composition has a linear burn rate of greater than or equal to about 23 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent of less than or equal to about 0.34.

In one aspect, the guanidine nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition. The basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition.

Advantageously, the present disclosure in yet other variations methods of forming a gas generant with reduced pressure sensitivity. The method may comprise mixing basic copper nitrate, guanidine nitrate, an alkaline earth zirconium oxide, and a liquid to form a mixture. The mixture is spray dried to form a powder. The powder is compacted to form the gas generant having a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent (n) of less than or equal to about 0.35.

In one aspect, the alkaline earth zirconium oxide is present at greater than or equal to about 0.1% to less than or equal to about 6% by mass of the gas generant. The guanidine nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant. The basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant. The gas generant is substantially free of potassium perchlorate.

In one aspect, the alkaline earth zirconium oxide is selected from the group consisting of: barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.

Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.

When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.

As used herein, unless otherwise indicated, amounts expressed in weight and mass are used interchangeably, but should be understood to reflect a mass of a given component.

Example embodiments will now be described more fully with reference to the accompanying drawings.

The present disclosure provides gas generant compositions for an automotive inflatable restraint system that comprise one or more fuels, such as guanidine nitrate, one or more oxidizers, such as basic copper nitrate, and an additive comprising an alkaline earth zirconium oxide. The present disclosure thus provides a method to achieve both higher burning rates and reduced pressure sensitivity by incorporating a new type of ceramic additive, a zirconate-based additive, in a pyrotechnic formulation that comprises basic copper nitrate and guanidine nitrate. Such a gas generant composition can be cool burning and have low flame temperatures at combustion, for example, having a maximum combustion temperature of less than or equal to about 1700 K (1,427° C.). Gas generants that provide certain fuel and oxidizer combinations, like basic copper nitrate and guanidine nitrate, with zirconate compounds maintain good performance, including good gas yields at relatively cool combustion temperatures, while exhibiting reduced pressure sensitivity and/or increased burn rate in comparison to comparative gas generants having the same components except lacking the zirconium oxide-based compound(s).

The alkaline earth zirconium oxide compound includes alkaline earth metals, namely elements of Group 2 of IUPAC Periodic Table, including barium (Ba), calcium (Ca), strontium (Sr), beryllium (Be), and/or magnesium (Mg). In certain aspects, the alkaline earth zirconium oxide compound is selected from the group consisting of: barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof. In certain other variations, the alkaline earth zirconium oxide compound comprises barium zirconate (BaZrO₃). The alkaline earth zirconium oxide may be present at greater than or equal to about 0.1% by mass to less than or equal to about 6% by mass of the overall gas generant composition, optionally at greater than or equal to about 0.5 to less than or equal to about 5% by mass of the total gas generant composition, and in certain variations, optionally at greater than or equal to about 4% to less than or equal to about 5% by mass of the gas generant composition.

The alkaline earth zirconium oxide may have a nominal average particle size of greater than or equal to about 0.1 micrometers (μm) to less than or equal to about optionally greater than or equal to about 1 μm to less than or equal to about 5 and in certain variations, optionally greater than or equal to about 1 μm to less than or equal to about 2 μm.

The gas generant composition comprises one or more fuels, which may include a primary fuel and one or more additional optional co-fuels, along with at least one oxidizer. Gas generant fuels may be selected to impart certain desirable characteristics to the gas generant formulation, such as gas yield, burning rate, thermal stability, combustion flame temperature, and the like. Suitable fuels can be organic compounds containing two or more of the elements: carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). The fuels can also include transition metal salts and transition metal nitrate complexes. Examples of fuels useful for gas generants according to the present disclosure include those selected from the group consisting of guanidine nitrate, diammonium 5,5′-bitetrazole (DABT), copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof. In certain variations, the fuel comprises guanidine nitrate (GuNO₃ or GN). The gas generant may comprise such fuel(s) at greater than or equal to about 10% by weight to less than or equal to about 80% by weight of the total gas generant composition. In one variation, a suitable cool burning gas generant composition optionally includes a total amount of fuels, including guanidine nitrate, at greater than or equal to about 15% to less than or equal to about 80% by weight, optionally at greater than or equal to about 25% to less than or equal to about 70%, optionally at greater than or equal to about 30% to less than or equal to about 60%, optionally greater than or equal to about 40% to less than or equal to about 55% by weight in the total gas generant composition.

Certain suitable oxidizers for the gas generant compositions of the present disclosure include, by way of non-limiting example, alkali metal (e.g., elements of Group 1 of IUPAC Periodic Table, including Li, Na, K, Rb, and/or Cs), alkaline earth metal (e.g., elements of Group 2 of IUPAC Periodic Table, including Be, Mg, Ca, Sr, and/or Ba), and ammonium nitrates and nitrites; metal oxides (including Cu, Mo, Fe, Bi, La, and the like); basic metal nitrates (e.g., elements of transition metals of Row 4 of IUPAC Periodic Table, including Mn, Fe, Co, Cu, and/or Zn); transition metal complexes of ammonium nitrate (e.g., elements selected from Groups 3-12 of the IUPAC Periodic Table); metal ammine nitrates, metal hydroxides, select perchlorates, such as ammonium perchlorate, and combinations thereof. One or more of these oxidizers are selected along with the fuel component to form a gas generant that upon combustion achieves an effectively high burn rate and gas yield. The gas generant may include combinations of oxidizers, such that the oxidizers may be nominally considered a primary oxidizer, a second oxidizer, and the like. In one embodiment, a suitable oxidizing agent for use in the gas generant comprises a basic metal nitrate, such as basic copper nitrate. Basic copper nitrate has a high oxygen to metal ratio and good slag forming capabilities.

Oxidizing agents may be respectively present in a gas generant composition in an amount of less than or equal to about 70% by weight of the gas generant composition; optionally less than or equal to about 60% by weight; optionally less than or equal to about 50% by weight; optionally less than or equal to about 40% by weight; optionally less than or equal to about 30% by weight; optionally less than or equal to about 25% by weight; optionally less than or equal to about 20% by weight; and in certain aspects, less than or equal to about 15% by weight of the gas generant composition. In certain variations of the present disclosure, the gas generant composition comprises a total amount of oxidizers of greater than or equal to about 25% to less than or equal to about 70% by weight and in certain variations, optionally greater than or equal to about 30% to less than or equal to about 60% by weight of the total gas generant composition.

In certain variations, the gas generant composition is substantially free of select perchlorates, such as potassium perchlorate. The presence of potassium perchlorate is believed to inhibit the desirable performance attributes otherwise provided by inclusion of an additive comprising an alkaline earth zirconium oxide compound in a gas generant composition, especially those that comprise guanidine nitrate and basic copper nitrate. The term “substantially free” as referred to herein means that the compound is absent to the extent that that undesirable and/or detrimental effects are avoided. In the present embodiment, a gas generant that is “substantially free” of a compound like potassium perchlorate comprises less than about 0.5% by weight of the compound, optionally less than about 0.1% by weight of the compound, optionally less than about 0.01% by weight of the compound, and in certain aspects, comprises 0% by weight of the of the compound. Gas generants that are substantially free of potassium perchlorate, but include the alkaline earth metal zirconium oxide additives, have significantly improved burn characteristics (e.g., higher burning rate and/or lower pressure sensitivity). In certain embodiments, the gas generant is substantially free of all perchlorate-containing oxidizing agents or stated in another way; the gas generant only includes perchlorate-free oxidizing agents.

When a perchlorate-containing oxidizing agent is present, it may be ammonium perchlorate, which is included in relatively low amounts. In certain aspects, when the ammonium perchlorate is included in the gas generant, the gas generant comprises less than or equal to about 7% by weight of the ammonium perchlorate, optionally less than or equal to about 5% by weight of the ammonium perchlorate, optionally less than or equal to about 3% by weight of the ammonium perchlorate, optionally less than or equal to about 2% by weight of the ammonium perchlorate, and in certain aspects, less than or equal to about 1% by weight of ammonium perchlorate. Generally, the effectiveness of an additive like barium zirconate (BaZrO₃) appears to be diminished if the ammonium perchlorate is present in a relatively smaller particle size and more effective when the ammonium perchlorate has a larger particle size. Thus, when the ammonium perchlorate has an average particle size of about 400 the ammonium perchlorate may be present in amounts of up to about 7% by weight of the total gas generant composition. Where the ammonium perchlorate is a relative small particles size, for example, having an average particle size of about 90 the ammonium perchlorate may be present in an amount of up to about 5% by weight of the total gas generant composition. If the smaller particle size ammonium perchlorate (e.g., having an average particle size of about 90 μm) is included at higher levels above 5% by weight, then the effectiveness of the alkaline earth metal zirconium oxide appears to be diminished, as will be discussed further below.

Where a secondary oxidizer, such as ammonium perchlorate, is included in combination with a primary oxidizer, such as basic copper nitrate, it may be limited to an amount of greater than or equal to about 1% by weight to less than or equal to about 7% by weight, optionally greater than or equal to about 1% to less than or equal to about 5% of the total gas generant composition to retain the cool burning properties of the gas generant.

A gas generant composition may optionally include additional components known to those of skill in the art. Such additives typically function to improve the handling or other material characteristics of the slag, which remains after combustion of the gas generant material; and improve ability to handle or process pyrotechnic raw materials. By way of non-limiting example, additional ingredients for the gas generant composition may be selected from the group consisting of: flow aids, pressing aids, metal oxides, and combinations thereof. If minor ingredients or additives are included in the gas generant, they may be cumulatively present at less than or equal to about 15% by weight of the total gas generant composition, optionally less than or equal to about 10% by weight of the total gas generant composition, optionally less than or equal to about 8% by weight of the total gas generant composition, and in certain variations, optionally less than or equal to about 5% by weight of the total gas generant composition. By way of example, such an additive may be selected from the group consisting of: flow aids, press aids, slagging agents, coolants, metal oxides, and any combinations thereof. Where present in a gas generant composition, in certain variations each respective additive may be present at greater than or equal to 0% to less than or equal to about 5% by weight; optionally greater than or equal to about 0.1% to less than or equal to about 4% by weight, and in certain variations, optionally greater than or equal to about 0.5% to less than or equal to about 3% by weight of the gas generant, so that the total amount of additives is less than or equal to about 4%.

In certain aspects, the alkaline earth metal zirconate additives not only improve burn rate and reduce pressure sensitivity, but also function as inert slagging agents, reducing particulate production during combustion of the gas generant composition. Thus, in certain variations, the gas generant composition may be substantially free of certain conventional slag forming agents or slagging agents. Specifically, the gas generants may be substantially free of refractory compounds such as silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), and combinations thereof. However, in alternative variations, the gas generant composition may further include conventional slagging agents, like aluminum oxide, silicon oxide, and titanium dioxides, refractory materials or other metal oxides that melt at or near the combustion flame temperature.

The gas generant compositions may optionally include a metal oxide that serves as a viscosity-modifying compound or an additional slag-forming agent (in addition to the slag-forming agent described above). Suitable metal oxides may include silicon dioxide, cerium oxide, ferric oxide, titanium oxide, zirconium oxide, bismuth oxide, molybdenum oxide, lanthanum oxide and the like.

Coolants for lowering gas temperature include basic copper carbonate or other suitable carbonates. Press aids used during compression processing, include lubricants and/or release agents, such as graphite, calcium stearate, magnesium stearate, molybdenum disulfide, tungsten disulfide, graphitic boron nitride, may be included in the gas generant compositions, by way of non-limiting example. Conventional flow aids may also be employed, such as high surface area fumed silica.

In certain aspects, a cool burning gas generant may be considered to have a maximum flame temperature at combustion (T_(c)) of less than approximately 1900K (1,627° C.), optionally less than or equal to approximately 1700 K (1,427° C.), and in certain variations, optionally less than approximately 1600K (1,327° C.). The cool burning gas generants of the present disclosure may have a relatively low maximum flame temperatures at combustion (T_(c)), for example, greater than or equal to about 1400K (1,127° C.) to less than or equal to about 1700K (1,427° C.) and in certain variations, optionally greater than or equal to about 1400K (1,127° C. to less than or equal to about 1600K (1,327° C.). Such cool burning gas generants have been shown to enable inflator devices with reduced filtration, which operate in a manner that provides adequate restraint and protection, without the risk of burns or injury to an automobile occupant in the event of a crash. Thus, minimizing flame temperature is advantageous. However, the alkaline earth metal zirconium oxide additive may be used in any gas generant and is not necessarily limited to cool burning gas generants.

In accordance with certain aspects of the present teachings, a gas generant composition is provided that includes an alkaline earth metal zirconium oxide additive having a volumetric gas yield of optionally greater than or equal to about 5.7 moles/100 cm³. The product of gravimetric gas yield and density is a volumetric gas yield. In certain embodiments, the volumetric gas yield is greater than or equal to about 5.8 moles/100 cm³ of gas generant, optionally greater than or equal to about 5.9 moles/100 cm³ of gas generant, optionally greater than or equal to about 6.0 moles/100 cm³ of gas generant, optionally greater than or equal to about 6.1 moles/100 cm³ of gas generant, and in certain variations, optionally greater than or equal to about 6.2 moles/100 cm³ of gas generant.

In certain variations, the gas generant has a mass density of greater than about 2 g/cm³, optionally greater than or equal to about 2.1 g/cm³, and in certain variations, optionally greater than or equal to about 2.2 g/cm³.

In addition to improved gas generant performance with respect to volumetric gas yield, relative quickness as determined by observed burning rate is also a consideration in inflator gas generant design.

In general, a common expression of burning rate law for a gas generant is as follows:

r _(b) =ae ^(bT) P ^(n)  (Eqn. 1)

where r_(b) is a burning rate as a function of temperature and pressure; a is a pressure coefficient, P is pressure, n is a pressure exponent, T is a temperature of the environment, and b is a sensitivity to temperature coefficient.

All of the parameters in the burning rate law can be graphically determined or calculated by performing burning rate experiments across a range of pressures and temperatures. a is the Y intercept of a plot of log R_(b) versus log P at constant T. The pressure exponent (n) is the slope of a linear regression line drawn through the log-log plot of linear burn rate (r_(b)) versus pressure (P) at constant T. b or as it is also commonly known, Op, can be calculated using the following equation:

$\begin{matrix} {\sigma_{P} = {{\frac{1}{R_{b}}\left\lbrack \frac{\delta R_{b}}{\delta T_{t}} \right\rbrack} = {\left\lbrack \frac{\delta \; \ln R_{b}}{\delta T_{t}} \right\rbrack.}}} & \left( {{Eqn}.\mspace{14mu} 2} \right) \end{matrix}$

In various embodiments, the gas generant provided by the present disclosure has a desirably high burning rate that enables desirable pressure curves for inflation of an airbag. A linear burn rate “r_(b)” for a gas generant material may be expressed in length per time at a given pressure. In accordance with various aspects of the present disclosure, the gas generant has a linear burn rate of greater than or equal to about 20 mm per second at a pressure of 20.7 megapascals MPa (or about 21 megapascals (MPa)). In certain embodiments, the burn rate for the gas generant is greater than or equal to about 21 mm per second at a pressure of about 21 MPa, optionally greater than or equal to about 22 mm per second at a pressure of about 21 MPa, optionally greater than or equal to about 23 mm per second at a pressure of about 21 MPa, and optionally greater than or equal to about 24 mm per second at a pressure of about 21 MPa.

One important aspect of a gas generant material's performance is combustion stability, as reflected by its burn rate pressure sensitivity. Gas generant materials exhibiting higher burn rate pressure sensitivity can potentially lead to undesirable performance variability, such as when the corresponding material or formulation is reacted under different pressure conditions. The gas generants of the present disclosure including the alkaline earth metal zirconium oxide additive desirably exhibit reduced or lessened burn rate pressure sensitivity. In certain aspects, a gas generant material having an acceptable pressure sensitivity has a linear burning rate slope or pressure exponent (n) of less than or equal to about 0.35, optionally less than or equal to about 0.34, optionally less than or equal to about 0.33, and in certain aspects, optionally less than or equal to about 0.32. A material having a linear burn rate slope of less than or equal to about 0.35 fulfills hot to cold performance variation requirements, and can reduce performance variability and pressure requirements of the inflator as well. Thus, in various aspects, it is desirable that the gas generant materials have a constant slope over the pressure range of inflator operation, which is typically about 1,000 psi (about 6.9 MPa) to about 5,000 psi (about 34.5 MPa) and desirably has a constant slope that is less than or equal to about 0.35.

Inclusion of an alkaline earth metal zirconium oxide additive in the gas generants provides the desired burn rates and pressure insensitivity during combustion. A gas generant may comprise an alkaline earth metal zirconium oxide additive at greater than or equal to about 0.1% by mass to less than or equal to about 6% by mass of gas generant composition, and may further comprise one or more fuels present at greater than or equal to about 10% to less than or equal to about 80% by weight of the total gas generant composition, optionally greater than or equal to about 30% to less than or equal to about 60% by weight of the total gas generant composition; one or more oxidizers present at greater than or equal to about 25% to less than or equal to about 70% by weight of the total gas generant composition, optionally greater than or equal to about 30% to less than or equal to about 60% by weight of the total gas generant composition; and one or more gas generant additives present at greater than or equal to 0% to less than or equal to about 15% by weight of the total gas generant composition, optionally greater than or equal to about 0% to less than or equal to about 8% by weight of the total gas generant composition. The gas generant composition is substantially free of potassium perchlorate. In certain variations, the gas generant composition may include one or more fuels selected from the group consisting of: guanidine nitrate, diammonium 5,5′-bitetrazole (DABT), copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, a melamine oxalate compound, and combinations thereof. One or more oxidizers may be selected from the group consisting of: basic copper nitrate, alkali metal or alkaline earth metal nitrates, alkali metal, ammonium perchlorate, metal oxides, and combinations thereof. In certain variations, the alkaline earth metal zirconium oxide additive may be present at greater than or equal to about 0.5 to less than or equal to about 5% by mass of the gas generant composition.

In another variation, a gas generant comprises an alkaline earth metal zirconium oxide additive at greater than or equal to about 0.1% by weight to less than or equal to about 6% by weight of the gas generant composition, and may further comprise guanidine nitrate fuel present at greater than or equal to about 10% to less than or equal to about 80% by weight of the total gas generant composition, optionally present at greater than or equal to about 25% to less than or equal to about 75% of the total gas generant composition, optionally present at greater than or equal to about 30% to less than or equal to about 60% of the total gas generant composition; basic copper nitrate oxidizer present at greater than or equal to about 25% to less than or equal to about 70% by weight of the total gas generant composition, optionally present at greater than or equal to about 30% to less than or equal to about 60% of the total gas generant composition, optionally present at greater than or equal to about 40% to less than or equal to about 55% of the total gas generant composition; and one or more gas generant additives present at greater than or equal to 0% to less than or equal to about 15% by weight of the total gas generant composition, optionally at greater than or equal to about 0% to less than or equal to about 8% by weight of the total gas generant composition. In certain variations, the alkaline earth metal zirconium oxide additive may be present at greater than or equal to about 0.5% by weight to less than or equal to about 5% by weight of the gas generant composition. The alkaline earth metal zirconium oxide additive may be selected from the group consisting of barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof. In certain variations, the gas generant composition is substantially free of potassium perchlorate. The gas generant may be substantially free of all perchlorate-oxidizer agents. In certain variations, the gas generant composition is substantially free of aluminum oxide and silicon dioxide.

In certain variations, the guanidine nitrate is present at greater than or equal to about 50% to less than or equal to about 65% by weight of the total gas generant composition. The basic copper nitrate is present at greater than or equal to about 40% to less than or equal to about 55% by weight of the total gas generant composition, and the one or more gas generant additives are present at greater than or equal to 0% to less than or equal to about 10% by weight of the total gas generant composition.

Such a gas generant may be cool burning and have a maximum flame temperature at combustion (T_(c)) of greater than or equal to about 1400K (1,127° C.) to less than or equal to about 1700K (1,427° C.). Further, such a gas generant may have a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 20.7 megapascals (MPa). The gas generant may also have a linear burn rate pressure exponent of less than or equal to about 0.35. In other variations, the gas generant composition has a gas yield of greater than or equal to about 5.7 moles/100 cm³.

In yet another variation, a gas generant comprises a gas generant composition for an automotive inflatable restraint system that comprises guanidine nitrate, basic copper nitrate; and greater than or equal to about 0.1% by mass to less than or equal to about 6% by mass of barium zirconate (BaZrO₃). The gas generant composition is substantially free of potassium perchlorate. In certain aspects, the barium zirconate (BaZrO₃) is present at greater than or equal to about 0.5% to less than or equal to about 5% by mass of the gas generant composition. The gas generant may have a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 20.7 megapascals (MPa) and a linear burn rate pressure exponent of less than or equal to about 0.35. Further, the gas generant may be a cool burning gas generant having a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1700K (1,427° C.). A gas yield of the gas generant composition may be greater than or equal to about 5.7 moles/100 cm³. In certain aspects, the guanidine nitrate is present at greater than or equal to about 50% to less than or equal to about 65% by weight of the total gas generant composition, the basic copper nitrate is present at greater than or equal to about 40% to less than or equal to about 55% by weight of the total gas generant composition, and the one or more gas generant additives present at greater than or equal to 0% to less than or equal to about 10% by weight of the total gas generant composition.

In certain aspects, the incorporate of an additive like BaZrO₃ provides a gas generant with a burn rates in excess of 23 mm/s at 20.7 MPa and further with a pressure exponent of less than 0.35, when incorporated into the gas generant in amount of about 3% to 4% by weight. This represents an improvement of about 20% in burning rate and a 9% reduction in pressure exponent compared to the standard additives, like SiO₂ and Al₂O₃, which are conventionally used in a cool burning gas generant composition.

The gas generant compositions according to various aspects of the present disclosure are advantageous in that they may be spray dried in normal production equipment. Gas generant compositions including the alkaline earth metal zirconate component have an increased burn rate and a reduced pressure exponent compared to conventional formulations, such as those containing additives like silicon dioxide (SiO₂) and/or aluminum oxide (Al₂O₃). The increased burning rate permits the incorporation of fewer tablets to achieve a similar gas mass flow rate and/or allows for increased mass flow rate from a conventional inflator. Such advantages can increase design flexibility for an airbag inflator. Moreover, the reduced pressure exponent results in reduced variability in a given airbag inflator which can lead to increased safety margins, material savings and performance improvements.

In certain aspects, components of the gas generant compositions provided in accordance with the present disclosure may be water soluble or capable of being processed as a slurry that can be spray dried to form granules. The granules or powder can then be compacted and consolidated to form a solid gas generant, such as a pellet or grain.

In various aspects, a gas generant body is formed from a gas generant powder created by a spray drying process. In certain aspects, first a mixture can be formed by mixing one or more fuels, one or more oxidizers; and an alkaline earth zirconium oxide, as described above. In certain aspects, the one or more fuels may comprise guanidine nitrate, the one or more oxidizers may comprise basic copper nitrate. Thus, the mixing may include mixing guanidine nitrate, basic copper nitrate, an alkaline earth zirconium oxide, and a liquid to form a mixture.

Suitable liquid carriers include aqueous solutions that may be mostly water; however, the carrier may also contain one or more organic solvents or alcohols. In some embodiments, the carrier may include an azeotrope, which refers to a mixture of two or more liquids, such as water and certain alcohols that desirably evaporate in constant stoichiometric proportion at specific temperatures and pressures. The carrier is selected for compatibility with the fuel, oxidizer, and other components, such as the zirconate additive, to avoid adverse reactions and further to maximize solubility of the several components forming the slurry. Non-limiting examples of suitable carriers include water, isopropyl alcohol, n-propyl alcohol, and combinations thereof.

The gas generant composition may be formed from an aqueous dispersion of one or more components that are added to an aqueous vehicle to be substantially dissolved or suspended (for example, dispersed and stabilized) as a stable dispersion of solid particles. The mixture of components forming the aqueous dispersion may also take the form of a slurry, where the slurry is a flowable or pumpable mixture of fine (relatively small particle size) and substantially insoluble particle solids suspended in a liquid vehicle or carrier. Mixtures of solid materials suspended in a carrier are also contemplated. Thus, the slurry contains flowable and/or pumpable suspended solids and other materials in a carrier.

The gas generant composition may be formed from an aqueous dispersion of one or more components that are added to an aqueous vehicle to be substantially dissolved or suspended (for example, dispersed and stabilized) as a stable dispersion of solid particles. Thus, the solution or dispersion may be in the form of a slurry. The liquid mixture may then be spray dried to form a powder. More specifically, the dispersion or slurry may be spray-dried by passing the liquid mixture through a spray nozzle in order to form a stream of droplets. The droplets may contact hot air to effectively remove water and any other solvents from the droplets and subsequently produce solid particles of the gas generant composition.

Then, the powder may be compacted to form the gas generant. In certain aspects, the gas generant has a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 20.7 megapascals (MPa) (approximately 21 MPa) and a linear burn rate pressure exponent (n) of less than or equal to about 0.35. The gas generant may have any of the gas generant compositions described above. In certain aspects, the gas generant composition is substantially free of potassium perchlorate.

The alkaline earth zirconium oxide, fuel(s), oxidizer(s), other optional ingredients described above may be present in the mixture or may be introduced in subsequent processing. Such ingredients may be provided in the amounts indicated above. In certain aspects, the gas generant is substantially free of potassium perchlorate and in other aspects, substantially free of all perchlorate-containing oxidizers. In certain aspects, the gas generant is substantially free of silicon dioxide, aluminum oxide, and combinations thereof.

Spray drying of such a liquid mixture may be accomplished using various spray drying techniques and equipment known to those of skill in the art. For example, suitable spray drying apparatuses and accessory equipment include those manufactured by Anhydro Inc. (Olympia Fields, Ill.), BUCHI Corporation (New Castle, Del.), Marriott Walker Corporation (Birmingham, Mich.), Niro Inc. (Columbia, Md.), and Spray Drying Systems, Inc. (Eldersburg, Md.). The spray-dried mixture forms a powder material. The powder is then pressed to produce grains of the gas generant composition.

The compositions of the present disclosure are thus advantageous in that they may be spray dried in normal production equipment, either with all components outlined above as a final composition. Alternatively, the alkaline earth zirconium oxide can be incorporated into a spray dried base powder comprising the other gas generant ingredients, such as the one or more fuels like guanidine nitrate, the one or more oxidizers, such as basic copper nitrate by dry blending the zirconate additive particles with the base powder. The mixture of spray-dried base powder and alkaline earth zirconium oxide additive is then pressed to produce grains or pellets of the gas generant.

Various embodiments of the inventive technology can be further understood by the specific examples contained herein. Specific non-limiting Examples are provided for illustrative purposes of how to make and use the compositions, devices, and methods according to the present disclosure.

Example 1

Four percent by weight powdered (nominal particle size 1-2 μm) BaZrO₃ is dry blended into a sample of spray dried gas generant powder comprising 46.62% by weight basic copper nitrate (bCN) and 53.38% by weight guanidine nitrate (GN) (designated “base powder”). Both the original base powder and the resulting blend of base powder containing the BaZrO₃ are subjected to a burn rate determination at multiple pressures. The burn rate of the base powder is found to be 14.2 mm/s at 20.7 MPa with a pressure exponent of 0.60. The burn rate of the BaZrO₃ containing sample is found to be 24.0 mm/s with a pressure exponent of 0.34.

Example 2

Various levels of the BaZrO₃ additive are blended with the same bCN/Guanidine nitrate spray dried gas generant powder (“base powder”) described in Example 1. Burning rates of the resulting mixtures are determined and are summarized in Table 1 below.

TABLE 1 BaZrO₃ level, % 1.5 3 5 Burning Rate (R_(b)) at 20.6 22.9 24.2 20.7 MPa, mm/s Pressure exponent (n) 0.39 0.36 0.36

Example 3

Guanidine nitrate (51.24%, 29.05 Kg), basic copper carbonate (44.76%, 25.38 Kg) and barium zirconium oxide (4%, 2.27 Kg) are slurry mixed with 56.7 Kg of water at 90° C. and spray dried. The burning rate is measured on the resulting spray dried powder. A burn rate of 23.3 mm/s at 20.7 MPa with a pressure exponent of 0.32 is obtained. This compares favorably with the results obtained in Example 1.

Examples 4 Through 12

The procedure of Example 1 is repeated with various additives to compare the burn rate and pressure exponent to that obtained with the gas generants including the barium zirconium oxide additive. The results are summarized in Tables 2 and 3. Examples 4-9 are comparative examples of gas generants, while Examples 10-12 are gas generants prepared in accordance with certain aspects of the present disclosure. Example 10 comprises BaZrO₃, Example 11 comprises CaZrO₃, and Example 12 comprises SrZrO₃.

TABLE 2 Example 4 5 6 7 Additive (4% by none SiO₂ Al₂O₃ Fumed Al₂O₃ and Weight) Fumed SiO₂ Burning Rate 14.2 19.6 21.1 19.2 (R_(b)) at 20.7 MPa, mm/s Burning Rate 0.60 0.41 0.40 0.38 pressure exponent (n)

TABLE 3 Example 8 9 10 11 12 Additive (4% by CaTiO₃ SrTiO₃ BaZrO₃ CaZrO₃ SrZrO₃ Weight) Burning Rate 23.5 23.5 24.0 21.4 20.6 (R_(b)) at 20.7 MPa, mm/s Burning Rate 0.40 0.38 0.34 0.35 0.32 pressure exponent (n)

In certain aspects, advantages of gas generants prepared in accordance with certain aspects of the present disclosure can be seen by comparing Comparative Examples 4-9 with Examples 10-12. For all examples, inclusion of any of the additives improves performance, at least marginally. However, alkaline earth zirconium oxide additives (e.g., Example 10 with BaZrO₃, Example 11 with CaZrO₃, and Example 12 with SrZrO₃) are superior to all of the other additives (including the CaTiO₃ in Example 8 and SrTiO₃ in Example 9) with respect to providing the lowest, most desirable pressure exponent behavior. In other words, the gas generants of the present disclosure have desirably low pressure sensitivity during combustion. Example 10 having BaZrO₃ also provides for the highest burning rate with a suitably low pressure exponent of all of the additives examined.

Examples 13-16

Either conventional SiO₂ or BaZrO₃ in accordance with certain variations of the present disclosure are blended into a baseline generant comprising bCN and guanidine nitrate in the amount shown in Table 4. Ammonium perchlorate having an average particle size of about 400 μm is included in Examples 15 and 16.

TABLE 4 Example 13 14 15 16 bCN 43.88 43.88 42.98 42.98 (% by Weight) GuNO₃ 53.12 53.12 52.02 52.02 (% by Weight) SiO₂ 3.0 — 3.0 — (% by Weight) BaZrO₃ — 3.0 — 3.0 (% by Weight) NH₄ClO₄ 400 μm — — 2.0 2.0 particle size (% by Weight) Burn rate (r_(b)), 19.3 21.3 19.4 21.4 mm/s at 20.7 MPa Slope, n 0.43 0.34 0.43 0.36

The burn rates are then measured both in the presence or absence of ammonium perchlorate. The barium zirconate additive is effective, including when the ammonium perchlorate is present.

Examples 17-19

In these examples, ammonium perchlorate having an average particles size of about 400 μm is added to gas generants containing BaZrO₃ reflected in Table 5. The testing reveals that the BaZrO₃ additive maintains a low pressure exponent at levels of 7% or less of ammonium perchlorate.

TABLE 5 Example 17 18 19 bCN 40.25 38.48 36.34 (% by Weight) GuNO₃ 51.75 51.52 50.66 (% by Weight) BaZrO₃ 3.0 3.0 3.0 (% by Weight) NH₄ClO₄ 5.0 7.0 10.0 400 μm particle size (% by Weight) Burn rate 20.9 20.1 19.6 (R_(b)), mm/s at 20.7 MPa Slope, n 0.34 0.38 0.43

Examples 20-22

In Examples 20-22, ammonium perchlorate having an average particle size of 90 μm is added to gas generants containing BaZrO₃ as shown in Table 6.

TABLE 6 Example 20 21 22 bCN 40.25 38.48 36.34 (% by Weight) GuNO₃ 51.75 51.52 50.66 (% by Weight) BaZrO₃ 3.0 3.0 3.0 (% by Weight) NH₄ClO₄ 90 μm 5.0 7.0 10.0 particle size (% by Weight) Burn rate (r_(b)), 19.8 19.4 18.6 mm/s at 20.7 MPa Slope, n 0.40 0.47 0.54

In these examples, it appears that the zirconate additive is less effective if the ammonium perchlorate is present in a smaller particle size of about 90 as compared to the previous examples where the particle size was 400 In this case, ammonium perchlorate is desirably kept to less than or equal to about 5%.

Examples 23-30

Finally, a zirconate additive, such as BaZrO₃ does not appear to be effective in the presence of potassium perchlorate having an average particle size of 90 μm (Table 7—Examples 23-26) or 10 μm (Table 8—Examples 27-30) in gas generants containing guanidine nitrate and basic copper nitrate. Both the burning rate and pressure exponent are dominated by the presence of the potassium perchlorate.

TABLE 7 Example 23 24 25 26 bCN 41.12 39.34 36.7 33.76 (% by Weight) GuNO₃ 52.88 52.66 53.3 53.24 (% by Weight) BaZrO₃ 3.0 3.0 3.0 3.0 (% by Weight) KClO₄ 90 μm 3.0 5.0 7.0 10.0 (% by Weight) Burn rate, 18.1 20.0 21.9 26.1 mm/s at 20.7 MPa (% Slope, n 0.53 0.50 0.47 0.43

TABLE 8 Example 27 28 29 30 bCN 41.12 39.34 36.7 33.76 (% by Weight) GuNO₃ 52.88 52.66 53.3 53.24 (% by Weight) BaZrO₃ 3.0 3.0 3.0 3.0 (% by Weight) KClO₄ 10 3.0 5.0 7.0 10.0 μm average particle size (% by Weight) Burn rate 19.7 20.6 24.3 32.0 (r_(b)), mm/s at 20.7 MPa Slope, n 0.49 0.68 0.64 0.52

The influence of potassium perchlorate is stronger with the 10 μm (smaller) particle size as compared to the 90 μm particle size and appears to negate any beneficial effect from the barium zirconate additive. In conclusion, gas generant formulations benefitting from the zirconate additive enhancement can also effectively incorporate ammonium perchlorate, but not potassium perchlorate. If ammonium perchlorate is included, a larger particle size, for example, greater than or equal to about 90 μm is desirable. If the particle size is larger, then the amount of ammonium perchlorate may be up to about 7% by weight of the formulation.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A gas generant composition for an automotive inflatable restraint system comprising: one or more fuels; one or more oxidizers; and an alkaline earth zirconium oxide, wherein the gas generant composition is substantially free of potassium perchlorate.
 2. The gas generant composition of claim 1, wherein the alkaline earth zirconium oxide is selected from the group consisting of: barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof.
 3. The gas generant composition of claim 1, wherein the alkaline earth zirconium oxide is present at greater than or equal to about 0.1% to less than or equal to about 6% by mass of gas generant composition.
 4. The gas generant composition of claim 1, wherein the alkaline earth zirconium oxide is present at greater than or equal to about 0.5% to less than or equal to about 5% by mass of the gas generant composition.
 5. The gas generant composition of claim 1 having a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa).
 6. The gas generant composition of claim 1 having a linear burn rate pressure exponent (n) of less than or equal to about 0.35.
 7. The gas generant composition of claim 1 having a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1700K (1,427° C.) and a gas yield of greater than or equal to about 5.7 moles/100 cm³.
 8. The gas generant composition of claim 1 that is substantially free of silicon dioxide, aluminum oxide, and combinations thereof.
 9. The gas generant composition of claim 1, wherein: the one or more fuels are selected from the group consisting of: guanidine nitrate, diammonium 5,5′-bitetrazole (DABT), copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, a melamine oxalate compound, and combinations thereof; and the one or more oxidizers are selected from the group consisting of: basic copper nitrate, alkali metal or alkaline earth metal nitrates, alkali metal, ammonium perchlorate, metal oxides, and combinations thereof.
 10. The gas generant composition of claim 1, wherein the one or more oxidizers comprises ammonium perchlorate at less than or equal to about 7% by mass of gas generant composition.
 11. The gas generant composition of claim 1, wherein: the one or more fuels comprise guanidine nitrate present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition; basic copper nitrate present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition; and further comprising one or more gas generant additives present at greater than or equal to 0% to less than or equal to about 8% by mass of the gas generant composition.
 12. A gas generant composition for an automotive inflatable restraint system comprising: guanidine nitrate; basic copper nitrate; and greater than or equal to about 0.1% to less than or equal to about 6% by mass of barium zirconate (BaZrO₃), wherein the gas generant composition is substantially free of potassium perchlorate.
 13. The gas generant composition of claim 12, wherein the barium zirconate (BaZrO₃) is present at greater than or equal to about 0.5% to less than or equal to about 5% by mass of the gas generant composition.
 14. The gas generant composition of claim 12 having a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent (n) of less than or equal to about 0.35.
 15. The gas generant composition of claim 12 wherein the barium zirconate (BaZrO₃) is present at greater than or equal to about 4% to less than or equal to about 5% by mass of the gas generant composition and the gas generant composition has a linear burn rate of greater than or equal to about 23 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent of less than or equal to about 0.34.
 16. The gas generant composition of claim 12, wherein: the guanidine nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition; and the basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant composition.
 17. A method of forming a gas generant with reduced pressure sensitivity, the method comprising: mixing basic copper nitrate, guanidine nitrate, an alkaline earth zirconium oxide, and a liquid to form a mixture; spray drying the mixture to form a powder; and compacting the powder to form the gas generant having a linear burn rate of greater than or equal to about 20 mm per second at a pressure of about 21 megapascals (MPa) and a linear burn rate pressure exponent (n) of less than or equal to about 0.35.
 18. The method of claim 17, wherein: the alkaline earth zirconium oxide is present at greater than or equal to about 0.1% to less than or equal to about 6% by mass of the gas generant; the guanidine nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant; the basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 60% by mass of the gas generant; and the gas generant is substantially free of potassium perchlorate.
 19. The method of claim 17, wherein the alkaline earth zirconium oxide is selected from the group consisting of: barium zirconate (BaZrO₃), calcium zirconate (CaZrO₃), strontium zirconate (SrZrO₃), and combinations thereof. 